Data storage devices employ rotating data storage media such as hard disk drives. In a hard disk drive, data is written to the disk medium using a write head which generates a high localized magnetic field that aligns magnetic domains within the disk in one of two directions. In some cases, the magnetization direction is up or down relative to the plane of the disk (perpendicular magnetic recording, or PMR). In other cases, the magnetization direction is within the plane of the disk. In all cases, this data may then be read-out with a read head. The write and read heads are typically integrated within a single assembly. To achieve steadily increasing data storage densities (typically measured in bits/inch), which are now at levels near 1012 bits/in2 (1 Tb/in2), the sizes of the recording magnetic regions on the disk have been reduced to nm levels.
The dimensions of magnetic grains are being steadily decreased by modifying the seed layer in order to reduce the distribution (σD) [where the “D” denotes diameter] of magnetic grain sizes to levels below 10 to 15% (where σD is a percent of the mean diameter <D>). Current HAMR media preferably employ a co-deposited granular L10 FePt—X, FePd—X, FePtAg—X, FePtAu—X, FePtCu—X, FePtNi—X, MnAl—X, etc., or L11 ordered CoPt—X, CoPd—X, etc. layer, where X are segregants including C, SiOx, TiOx, SiNx, BNx, B2O3 and other nitrides, oxides, borides, and/or carbides. Typical percentages of the co-deposited (typically by sputtering) segregants are in the range of 15 to 50 atomic %. Depositions are done at elevated temperatures in the range 300 to 700° C. to ensure that the highly anisotropic (Ku) chemically ordered L10 phase is formed in a chemical ordering transition from an initially isotropic A1 phase (see FIG. 3). FIG. 2 illustrates a typical HAMR media design. In the embodiments disclosed herein, it is individual magnetic grains which are patterned, where there will typically be approximately 8 to 15 grains per bit, although embodiments with approximately 4 to 10 grains per bit are also possible for higher storage densities. Thus no write synchronization is required since the magnetic grain patterning is not directly correlated with the sizes or locations of data storage bits on the medium. Since the size ranges of magnetic grains are decreased by embodiments of the invention, the signal-to-noise ratio may be improved, enabling smaller data storage bits leading to higher areal densities.
Thus it would be advantageous in a data storage system to reduce the grain size distribution to levels below 10 to 15%.
It is further advantageous to enable the growth of highly uniaxial perpendicular anisotropic magnetic material on a template capable of withstanding temperatures as high as 700° C.
It would also be advantageous to create data storage media with small thermally stable columnar grains which are chemically distinct and isolated.
It would be still more advantageous to control both the grain size and grain size distribution of FePt or other high uniaxial perpendicular anisotropy magnetic materials employed in HAMR media.